1. Field of the Invention
The present invention is directed to apparatus for coupling railway cars, and to methods of manufacture thereof. Specifically, features are described herein in connection with E-type and F-type yokes to provide improved stress profiles, leading to increased service life. Methods of making yokes and other components of the coupling apparatus, using investment casting techniques, are also described.
2. Description of Related Art
There are relatively few arrangements known for positioning railway draft gear between freight cars. In the United States, the arrangements commonly used are governed by standards set by the American Association of Railroads (“AAR”). In general, two cars in a freight consist are joined by heavy shafts extending from each car, known as couplers, and each coupler is engaged with a yoke housing a shock-absorbing element referred to as the draft gear.
Conventionally, the yoke is an elongated structure having two side sections extending from and joined by a tail portion. The side sections (sometimes referred to as “straps”) are joined at the opposite end by a head portion where the yoke is joined to the coupler with a key or pin. The draft gear is positioned between the side sections of the yoke, and between the tail portion and the head portion. The best-known yokes are the E-type and F-type. The E-type yoke is governed by the AAR S-143 Standard, SY 40AE or YS93AE, for a 24⅝ inch gear pocket, referred to herein as the “S-143 standard,” or simply as the “E-type standard.” The F-type yoke is governed by the S-149 standard. The yokes differ primarily in the design and orientation of the pin or key used to join the coupler to the yoke, with respect to the railway car, although there are other significant differences.
The coupler is joined to the yoke by means of apertures in the head portion of the yoke, sometimes referred to as the key slot or pin bore, through which a key or pin is passed connecting the elements. When the train is in motion, the yoke is in tension, and compressive forces are transferred to bearing surfaces positioned at opposed ends of the yoke where the draft gear is housed. There may be a plate intermediate the yoke and the draft gear at the front side of the tail portion, and there is also usually a plate positioned proximate the head portion of the yoke, bearing force from the front of the draft gear.
In practice, the separation of railway cars in a freight consist allows for a specified yoke length. Depending on whether the yoke is E-type or F-type, the length may be 41⅛″ or 37½″ respectively, as defined by the applicable AAR standard. The side sections of a yoke are subjected to tension and can stretch over time causing the yoke to become difficult to remove from the car, due to deformations of the straps. Therefore, two challenges addressed by the present invention involve dimensioning the yoke so that it is (i) more resistant to stretching during use and (ii) more easily removed after being stretched in use.
Portions of the yoke that are subjected to concentrations of stress are also susceptible to cracking and failure over time. These areas include the front of the key slot in E-type yokes, and the area where the side sections join the tail portion. Thus, another challenge addressed by the invention is the dimensioning of the yoke so that it will meet the requirements of the standard AAR specification, while at the same time improving the stress profiles in these areas, as well as other areas of the yoke.
A still further object of the invention is the development of methods of manufacture that permit improvement in the dimensional tolerances of the yoke, which in turn allows the above described sophisticated design elements to be incorporated. These manufacturing techniques are also found to improve the surface finish of the components made.
E-type yokes are described and claimed in U.S. Pat. No. 5,096,076 and U.S. Pat. No. 5,511,676, both of which are incorporated herein by reference. The yoke according to the present invention is expected to provide an improved stress profile in response to applied tensile loads as compared to these prior art yokes.